Biaxially oriented polypropylene (BOPP) film is an important part of capacitor. The key parameters (ash content, isotacticity, molecular weight, melt flow rate, isotactic sequence length) of polypropylene resin used as raw materials for BOPP films and their influence rules were summarized in this paper. At the same time, the existing production technology of BOPP capacitor film was summarized, and the methods to improve the performance of BOPP film were further reviewed. Finally, it is proposed that the future development of BOPP films for capacitors will focus on the ultra-low ash resin raw materials and heat resistant films.

A series of resins with ≥30% of solid content and about 4 000 mPa·s of viscosity and their polyimide films were prepared by introducing flexible 4,4′-oxobisphthalic anhydride (ODPA) or twisted non-coplanar structure 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) into the molecular structure of homophthalic tetracarboxylic acid dianhydride-4,4′-diaminodiphenyl ether (PMDA-ODA), and capped with a capping agent. The properties of the films were characterized by tensile testing machine, breakdown voltage tester, TMA, DMA, TGA, and cross-cut tester. The results show that when the solid content of the semi-rigid structure PMDA-ODA resin increases to 30% and the viscosity reduces to about 4 000 mPa·s, the film could not be formed due to the low molecular weight, and the PI film with good electromechanical properties can be prepared through introducing flexible monomer to improve the the polymer flexibility and using norbornene diacetic anhydride (NA) for capping. When continuing to increase the resin solid content and increase the proportion of flexible monomers, the electromechanical properties, heat resistance, ahd the adhesion on the copper sheet of the film decrease. The films with 30% of solid content, about 4 000 mPa·s of viscosity, 30% mole fraction of ODPA, and end-capped with NA show better electromechanical properties, heat resistance, and adhesion, which can be used as a impregnating varnish for insulation protection on the surface of substrate.

In this paper, the research progress on new eco-friendly insulating gases at home and abroad was reviewed, and the international mainstream promotion of perfluoroisobutyronitrile (C₄F₇N) gas and its application in electrical equipment were expounded emphatically. The gap and surface insulation characteristics of C₄F₇N gas mixture were summarized, and the design criteria of the related equipment insulation was proposed. The decomposition characteristics and gas-solid compatibility evaluation indices of C₄F₇N gas mixture under different operating conditions were analyzed. Additionally, the research progress on arc-quenching performance of C₄F₇N and its gas mixture and the development and application of a series of eco-friendly equipment were introduced, so as to provide a theoretical reference for the environmental protection upgrade of SF₆ electrical equipment in the current stage. Meanwhile, it was noted that the research and development efforts on new eco-friendly insulating gases with superior performance were still ongoing at home and abroad, which can provide technical support for the construction of a green and low-carbon power grid.

To solve the problem of poor thermal conductivity of polyimide (PI), PI was doped with hexagonal boron nitride (h-BN) modified by a surface wetting agent (F068) through in-situ polymerization, and then a series of h-BN/PI high thermal conductivity composites were prepared. The structure of h-BN/PI composites was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The thermal conductivity mechanism of h-BN/PI composites was explored by introducing the Y.Agari model, and the influence of modified h-BN filler doping content on the thermal conductivity, mechanical, heat resistance, and insulating properties of the composites was analyzed. The results show that with the increase of modified h-BN doping content, the thermal conductivity and thermal stability of h-BN/PI composites increase, while their tensile strength, elongation at break, and electric strength exhibit a significant downward trend. When the doping amount of modified h-BN is less than 30%, the influence of polymer crystal size factor on the thermal conductivity of the composites is dominant. When the doping amount of modified h-BN is higher than 30%, the influence of the free factor of the thermal chain formed by thermal conductive particles on the thermal conductivity of the composites is dominant. When the doping amount of modified h-BN is 50%, the thermal conductivity of h-BN/PI composite reaches 0.83 W/(m·K), the electric strength is 198.6 kV/mm, the 5% thermal decomposition temperature is 595℃, the tensile strength is 64.8 MPa, and the elongation at break is 10.4%.

Polyimide (PI) is a class of high-performance polymer materials containing π-conjugated imide ring in the main chain, and its size of the band gap is one of the main factors directly affecting the thermal stability, optoelectronic properties, dielectric properties and other properties of the material. The electrically powered diamine group and the electrically absorbing dianhydride group in the conventional PI molecular structure determine that the value of band gap is nearby 3.0 eV, which directly affects its performance in the field of high-temperature energy storage, high-frequency communication, electrical insulation, etc. Because of the excellent structural designability of PIs, the band gap of PIs can be adjusted by modulating the monomer combination/chain segment structure/space structure, and the above properties of PIs can be optimized. In this paper, based on the main research progresses of PI bandgap modulation reported in recent years, the main strategies of PI bandgap modulation were elaborated from the perspectives of polymer structure and adjusting polymerization process, respectively, and the difficult problems faced in PI bandgap modulation were discussed with the example of its application in the field of dielectric energy storage. Finally, the future development direction of PI bandgap modulation was discussed on the basis of current research status of PI bandgap modulation.

In the development of gas insulated switchgear (GIS) and gas insulated transmission lines (GIL) towards higher voltage and larger capacity, the insulation performance at the internal insulator's gas-solid interface is recognized as a critical factor affecting the operational safety of GIS/GIL equipment. To ensure the insulation safety of GIS/GIL equipment in engineering applications, it is imperative to elucidate the insulation failure mechanisms at the gas-solid interface and explore methods to enhance its insulation performance. In this paper, first, the research progress in the field of gas-solid interface insulation was reviewed, the mechanisms of dynamic charge behavior at the gas-solid interface and its influencing factors were analyzed, and methods for charge regulation at the gas-solid interface were introduced. Subsequently, the mechanism of insulation failure influenced by metal particles at the interface was discussed, and the motion characteristics of metal particles and their mitigation measures were summarized. Following this, the insulation characteristics at the gas-solid interface in environmental-friendly insulating gases were described, and the methods for electric field regulation and flashover voltage enhancement at the interface were summarized. Finally, the research directions for gas-solid interface insulation of insulator in GIS/GIL were outlined.

To address the challenges of epoxy resins in electrical insulation and flame-retardant applications, a phosphorus-containing bio-based flame-retardant resin—bis(methacryloyloxy-4-hydroxy-3-methoxyphenyl) phenyl phosphate (DGEBDB) was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and renewable vanillin, and cured materials were prepared through blending it (0%, 25%, 50%, and 75%) with bisphenol A epoxy resin (DGEBA). Their flame retardancy, thermal properties, mechnical properties, and electrical properties were analyzed. The results show that when the mass fraction of DGEBDB is 75%, the limiting oxygen index (LOI) of epoxy bending system increases from 22.6% to 34.2%, and the flame retardant grade achieves V-0 in UL 94 tests. Cone calorimetry reveals that the DGEBDB can reduce the heat release rate (HRR) and total heat release (THR), showing excellent fire suppression. Electrical properties tests show that the electrical properties of the cured epoxy maintain good when the mass fraction of DGEBDB is as high as 75%, which ensures the reliability of DGEBDB in electrical application. Mechanical properties indicate that with the increase of DGEBDB content, the flexural strength and tensile strength increase, indicating an increase in structural integrity and load bearing capacity of the cured epoxy. Therefore, the addition of DGEBDB significantly enhances the flame retardantcy of composite, while maintaining the excellent thermal, mechanical, and electrical properties of epoxy resin, and when the mass fraction of DGEBDB is 25%, the overall performance is the best, which has a better prospect for practical applications.

Using styrene-butadiene-styrene (SBS) as the resin matrix and SiO₂ as the filler, SiO₂/hydrocarbon high frequency hydrocarbon copper clad laminate with low dielectric loss were prepared by hot-pressing method using a double-roll open mill and a flat vulcanizing machine. The resin film forming method and the influence of different contents and morphologies of SiO₂ under the open mill film on the dielectric performance, peel strength, thermal conductivity, tensile performance, and water absorption rate of high frequency hydrocarbon copper clad laminate were explored. The results show that compared with the traditional solvent-based resin film method, the solvent-free film production using an open mill has obvious advantages in the molding of composite resins and material properties. With the increase of SiO₂ content, the dielectric constant and dielectric loss of the high frequency hydrocarbon copper clad laminate increase, while the peel strength and water absorption rate decrease. Under the same particle size and filling content of SiO₂, the dielectric constant, dielectric loss factor, and water absorption rate of spherical SiO₂/hydrocarbon high frequency hydrocarbon copper clad laminate are lower than those of angular SiO₂/hydrocarbon high frequency hydrocarbon copper clad laminate. When the mass fraction of spherical SiO₂ is 75%, the comprehensive performance of the carbon-hydrogen high-frequency board is relatively superior, with a dielectric constant lower than 3.3, a dielectric loss factor of 0.002 2, and a water absorption rate lower than 0.040%.

In this paper, the basic research and application progress of high temperature resistant epoxy molding compound (EMC) at home and abroad in recent years were reviewed. The property requirements of advanced power electronics on the molding compound, the high temperature degradation mechanism of traditional EMC, the relationship between structure and thermal stability of EMC, and the modification pathways for improving the thermal stability of EMC were presented. Especially, the development status of multi-aromatic ring (MAR) and naphthalene-containing EMC were reviewed. At last, the future development trends of high temperature resistant EMC for power electronic packaging were prospected.

To develop polyimide (PI)-based composite films with low dielectric constant (D_k), low dielectric loss (D_f), and high temperature resistance at high frequency, a water-soluble polyamic salt (PAAS) was prepared by adding organic base into the polyamic acid, which is the precursor of fluoropolyimide (FPI), and composite films were prepared by compounding low dielectric polytetrafluoroethylene (PTFE) concentrated dispersion with the dried PAAS to form a water dispersion system. The effects of PTFE content on the dielectric, thermal, and mechanical properties of the composite films were studied. The experimental results show that with the increase of PTFE content, the dielectric constant of the composite films decreases continuously, but there will be some effects on the thermal stability and mechanical properties. The dielectric constant of 50%PTFE/FPI reaches the minimum value (D_k=1.5@8.5 GHz), and the dielectric loss of 10%PTFE/FPI in the frequency band of 9.25-10.25 GHz is less than 0.005. The glass transition temperature of the composite films is in the range of 289-297℃, and the thermal decomposition temperature at 5% is higher than 508℃. The thermal expansion coefficient of 40%PTFE/FPI is as low as 59.67×10^-6 K^-1. The tensile strength of 20%PTFE/FPI is 70 MPa, the tensile modulus is 1.59 GPa, and the elongation at break is 7.7%.